Preparation Of Doped Carbon-Based Materials And Research On Electrocatalytic H₂O₂ Production Performance

Hydrogen peroxide（H₂O₂）with strong oxidizing ability is widely used for the removal of colored dyes from textile wastewater.The yield of H₂O₂ by two-electron oxygen reduction reaction（2e^–ORR）has become a favored research area.Metal-organic skeleton（MOF）-derived carbon-based materials have been widely studied for their advantages of large specific surface area and porous structure.However,most of the MOF-derived carbon-based materials have poor 2e^–ORR activity,controversial confirmation of the active site,and the mechanism of the doping elements is not clear enough.Therefore,in this work,heteroatom doping technique and nitric acid oxidation method are used to regulate the types and contents of functional groups on the surface of carbon-based materials,as well as to modulate the electronic structure of the active center and zeta potential,to explore the 2e^–ORR mechanism,and to establish the structural-performance relationship to improve the 2e^–ORR performance of such materials.Nitrogen and fluorine co-doped porous carbon embedded Co nanoparticle composites(Co _NP@FNC-w)were successfully prepared using cobalt zeolite imidazolium skeleton-67（ZIF-67）as the precursor and HF as the F source.In 0.5 M H₂SO₄electrolyte,the Co _NP@FNC-15 have 93.0%H₂O₂ selectivity,the production rate is as high as 4021.4 mmol g^-1 h^-1.It is shown that the introduction of F atoms can modulate the active site,the electronic structure of Co-Nx and the zeta potential of the catalyst,and promotes the O₂ adsorption in acidic environment.At the same time,due to electrostatic repulsion,the F atoms with highly negatively charged accelerate the desorption of OOH^*,thus avoiding further decomposition of OOH^*and improving the selectivity of the catalyst.Finally,a homemade H-type electrolyzer was used to construct the electro-Fenton system,and the in situ generated H₂O₂ degraded 80 mg/L Rh B by 97.7%in only 22.5 min,demonstrating its great potential in wastewater treatment applications.H₂O₂ is widely applied for the removal of colored dyes from textile wastewater,so it is important to develop catalysts for 2e^–ORR in alkaline solution.In this chapter,a series of O-NPC-T porous carbon materials containing oxygen functional groups were successfully synthesized by oxidizing ZIF-67-derived porous carbon materials with concentrated HNO₃.The H₂O₂ selectivity of O-NPC-120 in 0.1 M KOH solution is83.1%,the electron transfer number is 2.33,and the H₂O₂ yield is 2909.8 mmol g^-1 h^-1with a Faraday efficiency of 95.6%.It is shown that graphite-N and-COOH functional groups act as active sites for the reaction,and both of them work together to improve the performance of 2e^-ORR.In addition,the induction of-COOH modulates the hydrophilicity and zeta potential of the catalyst,which also favors the reaction.N,O,and F co-doped porous carbon fibers（O-FNPC-t）were prepared by HNO₃oxidation method using polyaniline as a precursor and polytetrafluoroethylene（PTFE）instead of HF as the F source.In 0.1 M KOH solution,O-FNPC-5 showed an electron transfer number of 2.11,a selectivity of 93.0%,an H₂O₂ yield of 4225.2 mmol g^-1 h^-1,and a Faraday efficiency of 88.3%.It is demonstrated that graphite-N and-COOH serve as the reactive active sites,and the introduction of F atoms and-COOH functional groups gives the catalyst the most suitable adsorption strengths for O₂ and OOH^*intermediates and improves the activity and selectivity of the catalyst.Finally,the in situ generated H₂O₂ degraded 30 mg/L of Rh B by 91.4%in 2.5 h in a homemade alkaline H-type electrolyzer.This direct degradation method avoids the drawbacks of the traditional electro-Fenton system,such as the need for p H adjustment,additional addition of H₂O₂,and the generation of iron-containing sludge,and provides a new idea for the application of catalysts.